Hydraulic brake control device



OC- 15, 1951 w. sTELzER 2,571,963

HYDRAULIC BRAKE CONTROL DEVICE F11ed July 21, 1947 2 SHEETS- SHEET 1 F/LZ. J0 5 3946415444/4034 515? gg F1524 gif- 1 @5 9a @7 /00 XQQQ.

Oct. 16, 1951 w, STELZER 2,571,963

HYDRAULIC BRAKE CONTROL DEVICE fv Filed July 21, 1947 l V2 SHEETS- SHEET 2 Patented Oct. 16, 1951 HYDRAULIC BRAKE CONTROL DEVICE William ,Stelzen Summit, N. J., assigner to Empire Electric Brake Company, Newark, N. J a corporation of New Jersey Application July 21, 1947, Serial N0. 762,372

, 8 claims. (o1. 18s-152) control mechanism, and `more particularly to a device for automaticallyadjusting hydraulically operated vehicle brakes. l

In the conventional -vehicle hydraulic brake system, a master cylinder is operative for forcing hydraulic fluid through the brakeslines to actuate wheel cylinders Vto apply the brakes. The brake shoes are normally held-out of operative position against suitable stops by the action of relatively strong return springs, and the brake shoes move to such positions when the brake pedal is released. For reasons well known in the art it is the customary practice to provide adjacentY the outlet of the master cylinder a residual pressure valve which is operative under normal conditions for maintaining a residual pressure in the brake lines of from 10 to 12 pounds per square inch. The brake shoe return springs, when the brake pedal is released, move the brake shoes into engagement with the stops and force fluid to return through the brake lines to the master cylinder. As soon as the pressure in the brake lines drops to the predetermined pressure for which the residual pressure valve is designed, such valve automatically closes to retain the pressure referred to in the brake lines.

Because of the use of stops for limiting movement of the brake shoes to off positions, it will be obvious that when the brakes are Areleased, the shoes return to predetermined off position. As the brake shoes wear, the distance through which they must move to contact the brake drums, progressively increases, and accordingly it is necessary from time to time to adjust the brakes of a motor vehicle due to the wearing of the brake shoes. As wear takes place, it requires the introduction of increasing amounts of fluid into the brake cylinders of hydraulic brakes to eiect full brake engagement, the brake shoes returning in a conven` tional device to the same normal position at each brake releasing operation.

It has been proposed to provide automatic adjusting devices which predetermine and limit movement of the brake shoes away from applied position whereby, regardless of brake wear, the displacement of fluid from the master cylinder or brake booster intothe brake cylinders to apply the brakes will always be the same. Such devices, of which I am aware, are mechanical in type and` are associated with the vehicle brakeshoes and operate through. the medium of ratchets, friction engaging surfaces, etc., to limit the movement of the brake shoes away from applied position.

Mechanical devices of the character referred to for automaticallyradjusting vehicles brakes are relatively complicated and expensive to manufacture, and substantial expense is involved in the installation of the devices as accessories, and in the assembling of the brake mechanisms where vehicles are factory-equipped with such devices. Moreover, in installations where it is necessary lto apply the brakes of vehicles for relatively long periods of time, the brake'drums expand substantially and consequently contract to a substantial extent when cooling. With mechanical brake adjusting devices of the character referred to, the releasing movement of the brake shoes is always the same, and where substantial drum expansion has occured, followed by the substantial contraction which takes place when the drums cool, the drums contract into frictional engagement with theshoes and cause excessive and needless wear.

The disadvantage of prior brake adjusting mechanisms of which I am aware is aggravated by the fact that relativer strong brake shoe return springs are employed, and the devicespreviously used for predetermining the distance of movement of the shoes away from the drums had to overcome the substantial tension of the return springs. Where contraction of the drum into engagement of the shoe occurs, therefore, adjusting devices of the character referred to will hold the brake shoes against the drum under substantially greater pressure than that which could be exerted by the conventional residual pressure, acting alone.

An important object of the present invention is to provide a simple and novel device for effecting adjustment of hydraulic brakes and wherein the device is connected in a hydraulic brake line to control the movement of brake uid instead of being arranged in direct association with the brakes themselves.

A further object is to provide a device of this character which permits the ilow to the brakes of whatever luid is necessary for full brake application, thus compensating for. possible leakage, but wherein the device limits the return flow of brake fluid, thus limiting movement of the brake shoes away from the drums.

A further object is to provide such a device which is not only cheaper to manufacture and install than mechanical brake adjusters, but which can be connected into'ailuid brake line at any desired or convenient'point.

animee A further object is to provide such a device which may be utilized in conjunction with the iiuid line leading to each individual wheel brake, or which may be placed in or adjacent the outlet of the master cylinder or in or adjacent the outlet of a power booster mechanism, thus rendering it necessary to use only a single brake adjuster for all of the wheels of the vehicle.

A further object is to provide a device of the character described which possesses all of the characteristics of a residual pressure valve, thus permitting the use of the device in conjunction with a master cylinder with the residual pressure valve omitted therefrom.

A further object is to yprov-ide a brake control device which permits the use of substantially weaker brake shoe return springs and Ytransfers to such springs the function of generating and predetermining the residual pressure in the -system while at the same time preventing an articial increase in pressure in the system under o brake conditions, thus preventing :theibrake shoes from engaging the brake drumsurlder any conditions except during brake application with a pressure in excess yof that which would be caused by the normal relatively low residual pressure.

A further object is to provide a hydraulic brake adjuster of the type referred to which functions automatically to release any pressure in the brake cylinders above the usual residual pressure, thus preventing excessive friction between the brake shoes and drums if the latter contract substantially after having been expanded through relatively long continued use.

Other objects and advantages of the invention will become apparent during the course of the following description. In the drawings I have shown several vembodiments of the invention. In this showing Figure l is a central longitudinal sectional view through one form of the device shown in the brake-released condition, parts being shown in elevation;

Figure 2 is a similar view showing the parts oi the device in the positions they will occupy in the maximum brake-,applied positions;

Figure 3 isa similar view of a modified form of the device, shown in the fully released position;

Figure 4 is a similar View showing a further modification of the device directly associated with a brake cylinder, parts being shown in elevation and the brake cylinder being broken away; and

Figure 5 is a view of an additional modication directly connected to the master cylinder of the brake system with the usual residual pressure valve omitted from the master cylinder.

Referring to Figure 1, the numeral lil designates a relatively small cylinder having a fitting l I tapped into one end thereof and seating against a plate l2 engaging a shoulder [3 in the cylinder l0. The plate l2 is provided with an off-center opening I4 for the flow of brake iiuid, in a manner to be described.

A union I6 is connected in the end of the tting ll and is mounted on the end of the fluid inlet pipe I1 for the device. As will be further referred to in detail later, the pipe l1 may be the hydraulic supply line for an individual brake; t may be the outlet pipe of the vehicle master cylinder; or it may be the outlet pipe of a power booster brake mechanism. The opposite end of the cylinder is connected through a union 20 to an outlet pipe 2l. If the pipe Il is an individual brake pipe, the pipe 2l will lead to an individual brake cylinder. If the pipe l1 is connected to the outlet of the master cylinder or a power booster brake mechanism, the pipe 2l will be the main supply line for all of the brakes and will be provided with the usual branch pipes.

A plunger 25 is slidable in the cylinder lil and iits relatively loosely therein so as to provide a slight clearance space 26 for the passage past the plunger 25 of brake :duid under conditions to be described. The clearance 25 and the corresponding clearances in the other figures of the drawing have been exaggerated for the purpose of illustration. A conventional 0 ring 2a is arranged ina recess 29 in the cylinder l and acts as a seal to prevent low of iiuid past the plunger 25 except when the latter is in the fully applied brake position of Figure 2, to be referred to later.

The plunger 25 is provided in one end with an axial bore 30 terminating in a valve seat 3| normally engaged vby a `ball check valve i32. This valve .is normally :seated by one end Qf a very light spring 34 the opposite en d of which engages a projection on a small axial-.plunger The opposite end of this plungerengages the plate l2 inthe oli-brake position.

The bore '30 communicates with a larger bore 3i which, in turn. communicates witha relatively large axial bore38 inthe plunger 25. The bores 31 and 38 form a shoulder Baengageable by an 0 ring 4G arranged in a cup 4I. The ring 43 also acts as a check valve and is normally seated by engagement with oneend of a spring 44 hav.- ing its opposite end engaging a-spring seat45 in the form of Aa snap'ring carried 4by the small plunger `35 and havinga gap 45 therein for the passage of fluid therethrough under certain conditions. The ring 45, under conditions to be described, engages Va seat 48Y having a pressed rit in the b ore 38.

As Ypreviously.Statedfthe Vparts. of the device are shown in the oli-brake position in Figure l. To normally retain the parts insuch position a return spring 50 is arranged in the cylinder l0 and surrounds an axial projection 5I on the plunger 25.

As will be furtherdescrlbed below in conjunction with Figure 5 wherein a modied form of the invention is shown in :a complete braking system, Ythe device shownin Figures 1 and 2 is adapted to control the flow of brake iiuid through the brake lines ,to conventional brake cylinders which operate the brake shoes having relatively weak return springs,.and;it is the latter `springs which generate the residual pressure which acts back through'theline 12| when the brakes are released. Thesegeneralfeatures of applicants brake control system willbecorne fully apparent later.

In the form of the device shown in Figure 3, a cylinder 55is DlTQvided at one end with a fitting 5S attached thereinto and-connected by a union 51 to the inletzpipe IT, corresponding to the inlet pipe previously described. The outlet pipe 2|, in this case, is connected by a union 58 to an oir-center bore 59 communicating with the interior chamber 56 of the cylinder 55 through a passage 6 l.

A plunger 65 is'slidable in the cylinder 55 and is very slightly smaller in diameter than the interior of the cylinder to provide a clearance or leakage space 66 for a purpose to be described. The body of the plunger 65, as is true of the plunger 25, has its corners Apreferably slightly rounded.. The plunger 55 ycarries `an axial exten- Vsion 68 slidable in a reduced bore 69. The extension 68 is very slightly smaller than the diameter of the bore 69 to provide a slight clearance space Iwhen the parts are in the off-brake position shown in Figure 3. As soon as brake i' -application is to be initiated by movement of the plunger 65 to the right, as shown in Figure 3, the passage of uid through the space 10 is prevented by engagement of an O ring 1| with the walls of the bore 69, the ring 1| being carried by the plunger extension 68 and normally slightly spaced from the adjacent end of the chamber 60.

'I'he plunger 65 is urged to the oil-brake position by a return spring 15. During the greater portion of the movement of the plungerV 65 the flow of brake fluid through the clearance 66 is vprevented by an 0 ring 16. However, when the plunger 65 is moved to the right to its extreme brake-applying position, the left hand end of the plunger 65, as viewed in Figure 3, slightly clears the O ring 19 to permit the flow of iluid through the clearance 66. In the fully on position of the brakes, the plunger 65 occupies with respect to the 0 ring 16a position corresponding to the position of the plunger 25 with respect to the ring 28 in Figure 2, as will be further described later.

. The plunger 65 is provided in one end with a relatively large bore 80 communicating with one end of a small bore 8| opening into the cylinder bore 69. A relief valve body 84 is mounted in the bore 80 and is provided with an axially projecting stem 85 mounted in the bore 8| and of non-circular construction or smaller than the bore 8| so as not to interfere with the passage of fluid therethrough under conditions to be described. The valve body 84 engages an O ring 86 to tend to hold the latter against the adjacent end ofthe bore 89 to act as a check valve relative to the bore 8|. A spring 88 urges the valve body 84 to the right, as viewed in Figure 3, and has one end engaging a seat 89 pressed into the bore 80 and provided with an opening 90. A further and simplified form of the device is illustrated in Figure 4 in direct connection with one of the wheel cylinders. The Wheel cylinder and associated elements are conventional, except that substantially weaker than the usual brake shoe return springs are employed and the stops for limiting return movement of the brake shoes are eliminated. The brake cylinder mechanism in Figure 4 comprises a cylinder 95 having pistons 96 therein connected by rods 91 to the brake shoes in the usual manner, the ends of the cylin der 95 being provided with the usual boots 98. The inner ends of the pistons 96 are provided with seals 99 engaged by a spring |00 to hold the seals 99 in position.

The cylinder 95 is carried by the brake plate, a portion of which is illustrated in Figure 4 and indicated by the numeral |0|. The cylinder 95 is provided with a laterally extending cylinder |02 shown in the present instance as being integral with the cylinder 95. The cylinder |02 has a bore |04 communicating with the chamber |05 between the pistons 96 through a passage |06.

A fitting |01 is threaded in the end of the vcylinder |62 remote from the cylinder 95 and is connected by a union |08 to a hydraulic fluid supply line |09.

A round cornered plunger ||2 is mounted in the cylinder |02 and is of slightly smaller diameter than the internal diameter of the cylinder |02 to provide a slight clearance space ||3. The

-plunger ||2 is arranged between volute springs lI I5 and H6. IThe plunger ||2 is not positively limited in its movement, and the spring ||6 has a higher rate-than the spring ||5 to limit its free height. The plunger ||2 occupies the oirbrake position shown in Figure 4, and the passage of uid through the clearance space 3 is normally prevented .by an O ring ||8. When the brakes are fully applied, the plunger bodily moves slightly beyond the O ring ||8, that, is, upwardly past such ring, as viewed in Figure 4, thus corresponding to the brake-applied position of the plunger 25 in Figure 2.

In Figure 5 of the drawings a still further modication of the invention has been shown', this time in conjunction with a master cylinder, with the wheel cylinders and the brake elements associated with one such cylinder diagrammatically represented. The purpose of Figure 5 is not only to show a modied form of the present invention, but also to fully illustrate how it can be used in conjunction with the master cylinder to function not only as a brake adjuster but also as a residual pressure valve, thus eliminating necessity for the use of a conventional residual pressure valve in the master cylinder. The cost of the installation in Figure 5, therefore, is little, if any, higher than a conventional hydraulic brake system since the use of a conventional residual Valve is eliminated.

In Figure 5 the master cylinder as a whole is indicated by the numeral |25 and includes the usual reservoir |26 and cylinder |21 in which is arranged a conventional piston |28 operated in the usual manner by a rod |29 extending through a boot |30 and having an adjustable eye |3| for connecting the rod |29 to the brake pedal. The bottom wall of the reservoir is provided with the usual iluid openings |32 and |33, and areturn spring |34 tends to hold the piston |28 in its normal position.

The cylinder |21 is provided with the usual outlet bore |36 from which the conventional residual pressure valve has been omitted. A tting |38 is tapped into the opening |36 and is connected to and supports the cylinder |40 of the present device. The ntting |38, of course, is provided with an axial passage |4| for the ow of brake fluid from the master cylinder into the cylinder |40 when the brakes are applied.

A plunger |45 is slidable in the cylinder |40 and its external diameter is slightly smaller than the internal diameter of the cylinder |40 to provide a clearance or leakage space |46. In the normal position of the parts in Figure 5, and throughout the greater portion of the movement of the plunger |45, leakage through the clearance |46 is prevented by an 0 ring |41 in the cylinder |40.

In the outer end of the cylinder |40 is arranged a compression spring |50 which urges the plunger |45 toward its normal position shown in Figure 5 in contact with a washer |5|. The plunger |45 is provided with a chamber |52 communcating with the chamber |53 in the end of the cylinder |40. Communication between the chambers |52 and |53 takes place through a passage |54 normally closed by a ball valve |55 urged to closed position by a spring |56. This spring seats against a washer |51 having a pressed t in the end of the chamber 52.

The outer end of the cylinder |40 is provided with a suitable fitting |60 through which the chamber |53 communicates with one end of the usual hydraulic fluid line |6| which branches as at |62 for communication with the individual brake cylinders |63.

actress 7 Figure .5 `.the preferred arrangement iin cer- 'tain respects of .elements .associated with .one vehicle' Wheel has been illustrated. 1t obviously is `preferred that the same .arrangement `be employed for all of .the wheels. vOne .of the `brake .cylinders |53 is illustrated .as having its Apistons .operable for actuating conventional brake shoes 16.5 pivoted at their lower 'ends as at ISE. These brake shoes are urged away from brake-applied .positions by a return spring 1.58, shown broken conventional brake drum |10.

Operation Referring to Figures l and 2, it will be understood that the pipe Yll may be directly connected 'to the master cylinder or to the outlet of a booster brake mechanism, in which case the present device will be located in the main supply line corresponding to the line I'l in Figure 5. Accordingly the pipe line 2l will be branched in the same manner as the pipes H52 in Figure 5 for connection with the individual Wheel cylinders, preferably associated with the parts described in connection with Figure 5. If desired, one of the devices may be located in each branch line leading il;

to a wheel cylinder, but this has been fou-nd to be unnecessary in practice, only one of the devices being required.

The device, of course, will always be iilledwith brake iiuid and the parts will normally occupy the positions shown in Figure l. When the brakes are to be applied, hydraulic fluid is forced through pipe il and through opening ld into the adjacent end of the cylinder li). lThe valve 32 beingclosed, the plunger 25 will start to move toward the right. The ring 2li will seal the plunger 3l and cylinder l and prevent leakage of fluid past the plunger.

The plunger 25 accordingly will move toward the right in Figure l, displacing fluid through the pipe 2l at the same rate that fluid'is introduced into the inlet end of the cylinder lo. If maximum brake application takes place, the plunger 25 will move to the position shown inFigure 2 at which point the rear end of the plunger 2.5 .barely clears the O ring 26. Since reasonable clearance exists between the plunger 25. and the inner wall of the cylinder lil, any uid thereafter necessary for fully applying the brakes will flow around the plunger 25. Particular attention is invited to the fact, therefore, that in applying the brakes the plunger 25 does not limit the amount of fluid which can flow into the brake cylinders to effect brake application.

It may be noted that in a brake application where the amount of fluid transmitted through pipe ll is greater than the amount of fluid displaced by the plunger 25, the latter does not necessarily have to move the full distance to a posij tive stop against the right hand end of the bore;

of the cylinder id as viewed in Figures l and 2. On the contrary, it moves only a sufficient distance to clear the O ring 28 to permit the passage of fluid around the plunger. As soon as the dow of fluid stops, the plunger, acting as; a, valve .'75

in cooperation with the 0 ring,28, assumes a lap position.

Immediately upon the releasing of the brake pedal, lthe .pressure existing in the pipe line l2l and accordingly in the outlet end of `the cylinder t0 will rstart the plunger v25 Ion its return movement. The plunger 25 continues its return movement to its normal position shown in Figure l and in so doing, measures the `quantity of hydrauli'c brak-e fluid which is permitted to return to the device through the line 2l. This 4operation lconsequently Ipredetermines the movement of the brake 'shoes away from the brake drum and prevents vthe Abrake shoes from returning to any predetermined position as is true in conventional practice. Under the latter practice, the distance which the brake shoes must move into braking engagement with'the drums increases progressively as the brake shoes wear. With the .present device, the brake shoes 'move a `predetermined distance from fully applied position rather than to .a predetermined normal position. The normal posi'on of the brake shoes accordingly progressively moves as the brake shoes wear, thus makingit unnecessary to leffect periodic adjustment of the partsza's is the customary practice.

The return springs of the brake slices are ten.- sioned to provide for the :generation of a predetermined residual pressure in the brake lines. The spring fili (Figures i and 2) resists a slightly greater hydraulic pressure than that produced by the return spring i633. The spring Sri .is `re1- atively weak, being only suiiciently strong to seat the valve 3?., the latter serving merely in the nature of a pump check valve in a manner described below.

ln the normal functioningI of the apparatus, the retraction of the plunger 25 to its normal position as in Figure l withdraws fluid through the line2l, freeing the brake return spring l'68 to `move the. brake shoes away from the drums. The fixed return movement of the plunger 25 determines the distance of movement of the brake shoes away from the drums and the tension ofthe spring Hi8 of each wheel brake mechahisrn determines the residual pressure in the system.

Assuming that the vehicle has been descending along a mountain road and frequent application of the brakes has been necessary, the brake drums l'll will become heated and will expand radially. Assuming that the vehicle is now at the bottom of such mountain and the brakes are released, the brake shoes will move a predetermined distance from the drums and will remain in such positions. Contraotion of the drums, upon cooling, may bring the drums into frictional engagement with the -brake shoes. If this occurs, the brake shoes will move inwardly and will exert pressure on .the pistons of the brake cylinders to displace fluid back through the pipe lines. Under such conditions both of the valves 32 and 4B (Figures. 1 and 2) will open to relieve such pressure and permit fluid to flow back to the master cylinder, through the booster brake4 mechanism if the device is used with such mechanism.

While the springs |68 predetermine the residual pressure in the system, the valve lil is adapted to open at only a slightly higher pressure, and accordingly under the extreme conditions just described. the present device prevents the generation of pressure in the system. substantially above a relatively lowv residual pressure. Accordingly excessiveV frictional` engagement between the brake shoes and brake drums is prevented under any conditions.

It has been stated above that the amount of fluid withdrawn from the brake cylinders at each releasing of the brakes is determined by the retractile stroke of the plunger in the cylinder Il). Thus, after the brake drums have contracted due to cooling, or the hydraulic uid is expanded in the brake lines dueto heating, the brake applying stroke of the plunger 25 is reduced to the point where the latter does not move beyond the ring 28 and consequently less than the normal amount of fluid will be displaced through the line 2|. Consequently, in the retractile movement of the plunger 25 an equally reduced amount of brake uid is released from the brake cylinders by such movement of the plunger 25. In order to establish the proper adjustment of the brakes, as when the full displacement of fluid by the plunger 25 is released from the brake cylinder, provision is made in the form of the pumping device including the plunger to pump a certain amount of fluid from the secondary or brake cylinder side to the primary or master cylinder side. Upon the releasing of the brakes, and prior to the return of the parts to the position shown in Figure 1, the plunger 35 is arrested by contact with the plate I2. Continued movement of the plunger 25 back to its normal position then causes displacement of fluid in the chamber 31 past the valve 40 into the chamber 38, or the primary side of the adjuster, the valve 32 being closed.

In the next brake application, when the plunger 2.5 moves to the right, the plunger 35 momentarily remains stationary and thus moves relatively out of the chamber 31 due to the force of the spring 44, until the snap ring contacts the seat 48, and during such relative movement of the plunger 35 out of the chamber 31, uid is drawn into the chamber 31 through the check valve 32.

'Thus while relief valve means (32, 4?!) are provided to relieve excessive hydraulic pressures caused by dragging brakes, the proper adjustment of the correct amount of uid released from the brakes is effected by the pumping mechanism during each brake application. The relief valves, as such, merely constitute a safety feature and are not ordinarily needed.

As previously stated, mechanical devices have been developed for effecting self-adjustment of the brake shoes of a vehicle. Such devices, however, are onen to two seriousobjections. In the rst place it is necessary to build the devices into the brake drums, thus rendering installation expensive and requiring a separate device for each wheel. Only one of the present devices need be employed for the usual four wheels of a motor vehicle, thus rendering it less expensive 10 move a predetermined distance from such expanded drums. When the drums contract to normal size, they engage the shoes with substan- 4 tial pressure and thus cause a dragging of the to manufacture. Moreover, it merely'is necessary f to tap into the brake line at any desired point and attach the present device with conventional fittings, and accordingly the present device need not be built in or designed with respect to other elements of the brake structure.

There is a second serious obiection to conventional brake adjusting. All such adiusters are designed to permit movement of the brake shoes only a predetermined distance from the drums when the brakes are released. When it is necessary to use the brakes excessively, as when descending long hills. the brake drums become heated and expand radially to a substantial extent. When the brakes are released, the shoes brakes with `a consequent excess wearing of the brake shoes. The releasing of the shoes from the drums is positively prevented, or strongly frictionally opposed by the brake adjusters and is v not affected in any way in hydraulic brake mechl0* anisms by the means employed for maintaining residual pressures in the brake cylinders.

In the form of the invention shown in Figure 3, there is a normal clearance at the point 10, but this clearance is promptly closed and sealed by the 0 ring 1| as soon as the plunger starts to move to the right upon the introduction of uid through the pipe |1. Fluid trapped in the chamber 69 is free to escape through passage 8|, the valve ring 8S opening whenever pressure in the chamber 69 overbalances the pressure in the inlet line I1.

The plunger E5 is free to move to a point corresponding to the brake-applied position of the i plunger 25 in Figure 2. In other words, the left .-hand end of the plunger 65 and the O ring 16 When the brakes are released, fluid is free tol move from the brake line 2| into the chamber 60 and since the chamber 69 is now sealed both by the ring 1| and by the seating of the valve ring 86, a vacuum will be created in the chamber E9. This -vacuum tends to prevent return movement of the plunger 65 to normal position. Howev'er, the fluid in the chamber 60, by virtue of the force ofthe brake release springs in the brake cylinders, develops pressure against the lright hand end of the body of the plunger 65 as viewed in Figure 3, and this pressure, assisted by the spring 15, exerts a force to the left against the plun'rer 65 several times greater than that necessary to break the vacuum in the chamber 59. Accordingly the plunger 65 will be positively moved to the left. When the plunger 65 has moved to a point adjacent its normal position, the ring 1| will move outof contact with the walls of the chamber 69 and uid in the chamber 59 will rush into the chamber 69 to satisfy the vacuum therein.

In the fully app ied brake position, the volume of the chamber B0 will be displaced into the wheel cylinders plus whatever iiuid flows around the plunger 65 when the latter passes the O ring 16,V the plunger 65 being movable past theo ring 'i6 as is true of the plungerY 25 in Figure 2' with respect to its ring 28. On the return movement or' the parts, the expanding capacity of the chamber 6B will draw thereinto a volume of fluid equal to the maximum capacity of such chamber, and the chamber S9 wi'l draw additional uid thereinto when the seal 1| is `released from the bore or chamber 69. Accordingly an ample volume of fluid will be Withdrawn from the wheel cylinders to prevent Contact of the shoes Ywith the drums.

The device shown in Figure 3 is adapted to function muchv in the same manner as that shown inFigures 1 and 2 to relieve contact between the brake shoes and drums if the latter contract into engagement with the shoes. By pumping up and down on the brake pedal several tmes through a short distance, fluid may be displaced from the chamber 69 through the passage 8| and upon return movement.- of the parts to nor mal position fluid. will; flow from` chamber Silin-tochamber 69. SeveraLsuch brakepedal movements. according-ly will.4 withdraw sufficient- Abra-ke il-uidfrom' the brake cylinders to insure the re-V lievingvr of allA ContactY between the brake` shoes andfdrums.

"EheY form of the device in- Figure 4 has beenl illustrated as. one. possible embodimentv of the dev-ice, but it is not preferred sincevit requires a special, formationv of the brake cylinders and requires the usev of, one of the devices for each vehicleivheel. The springs H and H6 tend to; hold the plunger H2 inY the normal position show-n. Whe-n thebrakes are applied, fluid ilows through pipe Illu to move thel plunger |-|2 and thus kdisplacetlfirough opening MBE a volume 'ofr u'ds corresponding to that entering the. device throughY pipe |09. Ater the plunger ||2 passes thel Ofring Uli, fluid can pass around the cleareance space I3 to whatever extent may be neces-Y sary for: fullbrake application.

Fluid entering the chamber "J5-forces the pis-v tons 9|;Y apart to. movethe rods El and apply thev brakes in the usual manner. brakes are released, the returnv spr-ings move'the pistons 96 toward eachv other to displace fluid from the-.chamber Ill.y through opening |86 to return the plunger ||,2` to itsy normal position. If. excess. pressure. occurs. in the chamber |135, the-plunger H2 wil1 move*downweudlyA as viewed iniFigureA; past the O ring to release the excess pressure untill the desired residual pressure isn reestablished. While theY particular installation in Figure 4 is-not preferred, thev plunger ||2 isk adaptedv tofunction not onlyv to displace-` iluid into the brake cylinder, but also to release excess pressure if it is built up in thebrake cyinder;

Normally, tbe plunger H2 returns to the posi-4 tion` shown inFieure 4to release the brake shoes` fory a predetermined movementv away from theY brake drum. Any tendencvfor theplunger H2` to moveI bevond itsnormal position results inreducing the loading of the springl H5; and in.` creasing the loading of the spring H6 to oppose, such action. Movementrof the plunger ||2- beyond its normal positionl can occur, therefore, only if' excessive pressure is established in the chamber m5, due to the contraction` of the brakedrums after thel latter have been unduly eX- panded. The device in Figure.4 4, therefore, is adapted toY act not only as a brake adiuster but also as a residual pressure valve; The device shownin Figure 4, however, does not permit manual withdrawing ofY iluid from the brake cylinder asY is true of the forms of the invention shown in Figures 1 and 2.

The device is shown in Figure 5 in a specific installation to function both as a brake adjuster andas a residual'pressure valve. It will be noted that the usual residual pressure valve is eliminated from the master cylinder in Figure 5. The brakes' are applied by depressing the brake pedal` (not shown) to move the piston |28 toward the left to displace uid through passage MIA. The pressure built up to the right of the plunger |45 moves this plunger to the left in engagement with the O ring |41. When the plunger |45 passes the' ring |41, fluid can flow through the clearance space |46 until' full brake application has been eiected bythe introduction of fluid into the brake cylinders |53.

When the brakes are released', fluid will be displacedfrom the brake cylinders |63 by action of the brake shoe return springs and willeffect When theY vice may be made similarly adjustable.

movement of the-plunger |455to the right in' measured predetermined movement of the brake shoes away from the brake drums to eliminate the necessity formanual adjustment of the brakes.

The spring |55 is ofsuch tension as to retain. theball |55' seated againstthefdesired residua-l;- pressure in the brake lines. If such pressure-increases, for example. upon contraction of thebrake drums after they have expanded, the ball- 155. will unseat and thus relieve such excessive pressure as in certain of the forms of the invention previously described. Itlwillbe noted', there#- fore, that the device'is capable ofA use directly with the master cylinder toY function both as a: brake adjusterand'as a residual pressure valve. As in the caseiof theusual residual pressure valve, thev present device permits. unlimited ilu-id to be` forced. into -the brake lines while normallyy meas'-v uring the-'returning amount. of il-udtoflimit the. clearancey between the brake shoes' and drums'.` However, the valve |55` functions under all conditions Vin the same manner Yas a conventional` residua-l pressure valve to preventundue'accumue lation of pressure in the brake lines.r

From the foregoingY it will befapparent that each, formof the invention functions to measure the amount of fluid which; is permitted to re turn from the brakel cylinders after each brake application. Thus the shoes are prevented from returning to a fixed predetermined position asv is conventional and return rather to anormalpesition which varies constantly asr wear; onv the brake shoes takes place. Certain of thev devices are adjustable as to the amount of' fluid' which is permitted to return and4 all forms of the de- For. example, movement or the parts in Figures l and 2V is limitedV by engagement oi thel small plunger 215.r with the plate or washer |'2 and this washer may ber or anyadditional thickness, pro- Y ,iecting into the cylinder t9.' as suggestedr in dotted lines in. Figure 2; to predetermine theA distance of return movement ofY the plunger 25 when the brakes; are released.-v The same is truey of the washer ll in Figure 5;.

The device is therefore not only highly adlvantageous over mechanical brake adjusters for the reasonsd stated, but also is adapted to serve as a" residual: pressure valve, and the adjustment ofT the return movement ofthe plunger permits the same` size device to be used onv vehicles with varying brake systems. The device also isihigh ly: advantageous for an additional and: wholly non-obvious reason. As previously stated, the

device may be arranged.' inv the outlet of any conventional type of booster brake mechanism to normally govern the quantity of fluid returningY to the high pressure end of the boos-,ter and thus normally determinethe clearance between the brake shoes and the brake drums. In the manufacture of booster brake mechanisms it has been necessary to make such mechanisms inv a substantial variety of sizes to take care of different brake installations and to insure the max-L mum necessary displacement of hydraulic brake fluid for applying the brakes as the brake'Y shoes become worn. The use'of' the present device inmeteringthe flow of hydraulic brake iiuid makes it unnecessary for booster brake mechanisms/to take care of maximum demands as under present conditions since it is never necessary for such mechanisms to supply more liquid than is predetermined by movement of the plunger of either form of the present device plus whatever minor quantity of uid is necessary to compensate for leakage. The use of the present device with booster brake mechanisms' accordingly reduces the number of different sizes and designs of such mechanisms which need be manufactured.

In each case, the plunger is normally sealed by an ring and is adapted to assume a position in lapped relationship therewith for the escape past the plunger of whatever iiuid may be necessary for full brake application. Therefore the present device does not in any sense limit'the supply of fluid to the brake cylinders. However, the device normally limits the withdrawal of iluid from the brake cylinders, thus limiting the distance of movement ofi brake shoes away-'from the drums. If conventional brake shoe return springs are employed, it will be necessary that the springs 44 (Figure l), 83A (Figure 3), ||5- Figure 4) `and |56 (Figure 5) be sufciently strong to withstand the substantial pressure which'would be generated by the return springs. lThe present system permits the use of relatively weak return springs; as stated, and thus the brake shoe return springs are wholly depended upon to generate and predetermine the residual pressure. Such pressure is normally generated by the strong return springs customarily used, but the residual pressure is not determined by such springs since they move the brake shoes into engagement with stop elements. The residual pressure is normally determined by the master cylinder Valves provided for this purpose. The combination of the present device with return springs of proper tension for the` brake shoes predetermines the distance of movement of the shoes from the drums and depends solely on the return springs for generating the residual pressure.

As previously stated, where a single device of the present type is used in the main hydraulic uid supply line, it is necessary that all of the return springs |68 be of fairly equal tension. It will be obvious that if any onel return spring should exceed the tension of the other springs, the strongest spring would predetermine the residual pressure in the system and would maintain the brake shoes associated with the other return springs in engagement Vwith the brake drums. However, present Amethods of manufacturing springs have been soA highly developed as to accuracy that return springs which are reasonably identical with each :other readily may be obtained. Actually, a variation, of one pound between the minimum and maximum tensions of the various springs |68 is practicable since the brake shoes associated with thev weaker springs would be heldin very light contact with the brake shoes. It is entirely possible, however, to obtain return springs which vary only to the slightest extent from each other.

As previously stated, the brake return springs |68 are solely depended upon to generate the residual pressure in the system. The present device requires no stop means to limit movement of the brake shoes away from the drums. The brake shoes themselves, therefore, are movable away from the brake drums an indeter- 14 A minatedistance,.,b'ut such distance is predeterm'inedby the metering ofV the return vof fluid from the brake cylinders by the present device andV whenV the return ow of fluid is stopped by .the metering device, the return springs IGR determine the residual pressure.

I claim:

1. For use in a hydraulic braking system `having. brake-applying means, and means for supplying hydraulic brake fluid under pressure to said brake-applying means to apply the brakes, a brake control device comprising a metering device to limit to a predetermined quantity the amount of hydraulic uid returning from said brake-applying means upon the releasing of pressure iin the fluid-supplying means, and pumping me'ans for bleeding a relatively small amount of fluid from said brake-applying means to `thefluid supplying means upon each operation of Ythe brake-applying means.

.2; For use ina hydraulic vehicle braking system having a brake-applying device, a fluid pressure generating device and a hydraulic line connecting said Aiiuid pressure reducing device and said brake-applying device, a metering device in said hydraulic line and comprising a member movable in one direction when hydraulic iiuid'is transferred from said pressure-generating device to said brake-applying'device and movable in the opposite direction when the pressure in" said pressure-generating device is released, said movable member being operative in said first direction of'movement to render said fluid pressuregenerating device operative for transmitting to said brake-applying means a quantity of hydraulic iiuid uncontrolled by said movable member, said movable member being operative in its second-named direction of movement for metering the amount of fluid returning from said brake-'applying device to said fluid Vpressure generating device, and a pump carried by said movable member and automatically operative once during each movement thereof in said rstnamed direction and in said second-named direction for transferring a small amount of hydraulic fluid from said brake-applying device to said uid pressure generating device.

3. For use in a hydraulic vehicle braking system having a brake-applying device, a iiuid pressure generating device and a hydraulic line connecting said fluid pressure reducing device and said brake-applying device, a` metering device in said hydraulic 1ine and comprising a member movable in one direction when hydraulic uid is transferred from said pressure-generating device to said brake-applying device and movable in the opposite direction when the pressure in usaid pressure-generating device is released, said movable Amember being operative in said i'lrst direction of movement to render said uid pressure generating device operative for transmitting to said brake-applying means a quantity of hydraulic fluid uncontrolled by said movable m'ember, said movable member being operative in its Vsecond-named direction of movement for metering the amount of iiuid returning from said brake-applying device to said fluid pressure generating device, and a pump carried by said movable member and automatically operative once during each movement thereof in said rstnamed direction and in said second-named direction for transferring a small amount of hydraulic fluid from said brake-applying device to said fluid pressure generating device, said pump including valve means automatically operative when the 'pressure in. said. brake-applying device exceeds 'to a. predetermined extent the pressure in said iluid pressure generating device to :provide for the transfer. ofi hydraulic fluid from said brakeapplyin'g device to said fluid pressure generating device.

4. In combination, a hydraulic braking. system comprising brake-applying means, hydraulic fluid pressure producing means hydraulically connected thereto, a brake elementy operable by saidV brakeeapplying means, a rotatable element engageable by said'. brake element, said. brake elementfbeing biasedv away from said rotatable element and movable therefrom an indeterminate distance', an automatic brake adjuster having iiuid displacing meansA interposed between said pressure-producing means and said brake-applying means, means to effect a by-pass of fluid said' pressure-producnig means to said brake-applying means when said uid displacing meanshas moved a predetermined distancel in one' direction, and means responsive toY movement of said fluid-displacing meansV to pump a relatively small amount of iiuidi from said brake-applying means to said pressure-producing means..

I'ncombination, a hydraulic braking system hav-ing aA pressure-producing device, a brake element, a wheel' cylinder to receive pressure fluid from. said pressure-producing device to actuate said: brake element, a drum engageable by' said brake element, resilient means biasingk said brake element away'frcm said drum, saidbrake element being movableA from said drumt an indeterminate distancel whereby saidV resilient means predetermines the'residualpressure in the braking system, a casing interposed. between said pressure producing meansv andV said brake cylinder, a member in said casing having a normal position from which it is movable by' fluid from. said pressure producing; means to displace fluid into said brake cylinden means for effecting aleak-age of fluid past said movable member to said wheel cylinder after a predetermined amountof fluid has been displaced intosaid Wheel cylinder by said mov'- able member, and pumping means operative when said movable member isl actuated to transfer a smallamount of iiuid from said wheel cylinder to said pressure-producing means. r

6'. The-combination defined in claim 5 provided with a relief valve to limit residual pressureto the maximum predetermined by said resilient means.

'LA A hydraulic brake control. device comprising a cylinder adapted to be arranged in a hydraulic brake. line and having inlet and outlet ends com.- municating with such lines, a main plunger in said cylinder having clearance with respect to thei inner Wall thereof and normally arranged at alimit ofV movement toward said inlet end and being. movable toward said outlet end, a sealing ring carriedl by said cylinder and engaging said mainl plunger until the latter approaches said outlet end, whereupon such plunger becomes free of said sealing ring for the flow of hydraulic` aY plurality of successive axial bores communicat# ing with each: other and. with said inletV and outlet ends; an auxiliary plunger within said main plunger; a ball check valve normally closing communication' through one of said bores, a spring arranged between said auxiliary plunger and'said check valveto normally retain the latter seated toward said outlet end, a spring arranged in one of said bores' and seated with repsect to said auxiliary plunger, and a SecondY check valve controlling communication through said bores and urged to closed position toward said outlet end by said second-named spring.

8. A hydraulic brake control device comprising a main cylinder adapted to be connected at its ends in a hydraulic brake line, one end of said main cylinder comprising an inlet end, said main cylinder being provided' with a metering chamber portion and with an outlet chamber communicating with said metering chamber portion and with said brake line, a plunger reciprocal in said main cylinder and normally occupying a position. adjacent said inlet end, said main cylinderV having an axial auxiliary cylinder and said plunger having an axial extension projecting partly into and having clearance with said auxiliary cylinder when said plunger is in said normal position, an auxiliary sealing ring carried by saidl axial extension and movable into said auxiliary cylinder to close said clearance upon initial movement of'said plunger from normal position, and a main Sealing ring carried by said main cylinder and engaging said plunger when the latter" is in its normal position and throughout the greater portion: of the travel of said plunger toward said auxiliary chamber, said plunger beingY movable toward said. auxiliary chamber to such an extent that it Wholly clears said main sealing ring and having clearance relative to the walls of saidV main cylinder for the movement of fluid past saidV plunger when the latter passes said' main sealing ring, said plunger having an axial' passage communicating at its opposite ends with said inlet end and' with said auxiliary cylinder, and a spring pressed check valve controlling said axial passage and seating towardl said auxiliary cylinder.

WILLIAM STELZER.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number' Name Date 697,140 Goldschmidt Apr. 8, 1902 1,885,580 Bradbury Nov. l, 1932 2,345,811 Harp* Apr. 4, 1944 2,385,625 Hopmans Sept. 25, 1945 2,4%",178 Walley, Jr.V Aug. 20, 1946 FOREIGN PATENTS Number Country- Datel 1,570 Great Britan 1861 157,887 Austria Feb. 10, 1940 358,126 Great Britain Oct. 8, 1931 

